Contact

Description

The Contact block can be used to specify parameters related to mechanical contact enforcement in MOOSE simulations. The ContactAction is associated with this input block, and is the class that performs the associated model setup tasks. Use of the ContactAction is not strictly required, but it greatly simplifies the setup of a simulation using contact enforcement. A high-level description of the contact problem is provided here.

This block can be used to specify mechanical normal and tangential contact using several possible models for the physical behavior of the interaction:

frictionless
glued
coulomb (frictional)

Contact enforcement using node/face primary/secondary algorithms is available using the following mathematical formulations:

kinematic
penalty
tangential penalty (kinematic normal constraint with penalty tangential constraint)
augmented lagrange
reduced active nonlinear function set (RANFS)

In addition, face/face contact using a mortar method can also be specified using this block.

Constructed Objects

The primary task performed by this action is creating the Constraint classes that perform the contact enforcement. The type of Constraint class(es) constructed depend on the formulation and physical interaction model specified using the formulation and model parameters. Table 1 shows the Constraint classes that can be created for various types of contact enforcement.

Table 1: Constraint objects constructed by ContactAction

Formulation	Model	Constraint Object
kinematic	all	MechanicalContactConstraint
penalty	all	MechanicalContactConstraint
tangential_penalty	all	MechanicalContactConstraint
ranfs	frictionless	RANFSNormalMechanicalContact
mortar	all	MechanicalContactConstraint
mortar	all	NormalMortarMechanicalContact NormalMortarLMMechanicalContact
mortar	coulomb	TangentialMortarMechanicalContact TangentialMortarLMMechanicalContact

In addition to the Constraint class, several other objects are created, as shown in

Table 2: Other objects constructed by ContactAction

Constructed Object	Purpose
ContactPressureAux	Compute contact pressure and store in an AuxVariable
Penetration	Compute contact penetration and store in an AuxVariable
NodalArea	Compute nodal area and store in an AuxVariable

Notes on Node/Face Contact Enforcement

The node/face contact enforcement is based on a primary/secondary algorithm, in which contact is enforced at the nodes on the secondary surface, which cannot penetrate faces on the primary surface. As with all such approaches, for the best results, the primary surface should be the coarser of the two surfaces.

The contact enforcement system relies on MOOSE's geometric search system to provide the candidate set of faces that can interact with a secondary node at a given time. The set of candidate faces is controlled by the patch_size parameter and the patch_update_strategy options in the Mesh block. The patch size must be large enough to accommodate the sliding that occurs during a time step. It is generally recommended that the patch_update_strategy=auto be used.

The formulation parameter specifies the technique used to enforce contact. The DEFAULT option uses a kinematic enforcement algorithm that transfers the internal forces at secondary nodes to the corresponding primary face, and forces the secondary node to be at a specific location on the primary face using a penalty parameter. The converged solution with this approach results no penetration between the surfaces. The PENALTY algorithm employs a penalty approach, where the penetration between the surfaces is penalized, and the converged solution has a small penetration, which is inversely proportional to the penalty parameter.

Regardless of the formulation used, the robustness of the mechanical contact algorithm is affected by the penalty parameter. If the parameter is too small, there will be excessive penetrations with the penalty formulation, and convergence will suffer with the kinematic formulation. If the parameter is too large, the solver may struggle due to poor conditioning.

`System` Parameter

The system parameter is deprecated and currently defaults to Constraint.

Gap offset parameters

Gap offset can be provided to the current contact formulation enforced using the MechanicalContactConstraint. It can be either secondary_gap_offset (gap offset from secondary side) or mapped_primary_gap_offset (gap offset from primary side but mapped to secondary side). Use of these gap offset parameters treats the surfaces as if they were virtually extended (positive offset value) or narrowed (negative offset value) by the specified amount, so that the surfaces are treated as if they are closer or further away than they actually are. There is no deformation within the material in this gap offset region.

Multiple contact pairs

Users may need to set up mechanical contact between multiple contact pairs. For that application, users can provide arrays of primary and secondary boundary names which will match consecutively to define mechanical contact pairs. The same contact-related input parameters will be applied to all contact pairs defined in the action input.

note

The multiple contact pairs feature is not yet available for mortar contact.

[Contact]
  [action_name]
    primary = '20 20'
    secondary = '10 101'
    penalty = 1e7
    formulation = penalty
    tangential_tolerance = 0.0001
  []
[]

Example Input syntax

Node/face frictionless contact:

[Contact]
  [./leftright]
    secondary = 3
    primary = 2
    model = frictionless
    penalty = 1e+6
    normal_smoothing_distance = 0.1
  [../]
[]

Node/face frictional contact:

[Contact]
  [./leftright]
    secondary = 3
    primary = 2
    model = coulomb
    penalty = 1e+7
    friction_coefficient = 0.2
    formulation = penalty
    normal_smoothing_distance = 0.1
  [../]
[]

Normal (frictionless) mortar contact:

[Contact]
  [leftright]
    secondary = 10
    primary = 20
    model = frictionless
    formulation = mortar
    c_normal = 1e-1
  []
[]

Normal and tangential (frictional) mortar contact:

[Contact]
  [mortar]
    primary = 'bottom_top'
    secondary = 'top_bottom'
    formulation = mortar
    model = coulomb
    friction_coefficient = 0.4
    c_normal = 1e4
    c_tangential = 1.0e4
    interpolate_normals = false
  []
[]

Gap offset:

[Contact]
  [./leftright]
    primary = 2
    secondary = 3
    model = frictionless
    penalty = 1e+6
    secondary_gap_offset = secondary_gap_offset
    mapped_primary_gap_offset = mapped_primary_gap_offset
  [../]
[]

Input Parameters

primaryThe list of boundary IDs referring to primary sidesets
C++ Type:std::vector<BoundaryName>
Controllable:No
Description:The list of boundary IDs referring to primary sidesets
secondaryThe list of boundary IDs referring to secondary sidesets
C++ Type:std::vector<BoundaryName>
Controllable:No
Description:The list of boundary IDs referring to secondary sidesets

Required Parameters

active__all__ If specified only the blocks named will be visited and made active
Default:__all__
C++ Type:std::vector<std::string>
Controllable:No
Description:If specified only the blocks named will be visited and made active
al_frictional_force_toleranceThe tolerance of the frictional force for augmented Lagrangian method.
C++ Type:double
Controllable:No
Description:The tolerance of the frictional force for augmented Lagrangian method.
al_incremental_slip_toleranceThe tolerance of the incremental slip for augmented Lagrangian method.
C++ Type:double
Controllable:No
Description:The tolerance of the incremental slip for augmented Lagrangian method.
al_penetration_toleranceThe tolerance of the penetration for augmented Lagrangian method.
C++ Type:double
Controllable:No
Description:The tolerance of the penetration for augmented Lagrangian method.
c_normal1e+06Parameter for balancing the size of the gap and contact pressure for a mortar formulation. This purely numerical parameter affects convergence behavior and, in general, should be larger for stiffer materials. It is recommended that the user tries out various orders of magnitude for this parameter if the default value generates poor contact convergence.
Default:1e+06
C++ Type:double
Controllable:No
Description:Parameter for balancing the size of the gap and contact pressure for a mortar formulation. This purely numerical parameter affects convergence behavior and, in general, should be larger for stiffer materials. It is recommended that the user tries out various orders of magnitude for this parameter if the default value generates poor contact convergence.
c_tangential1Numerical parameter for nonlinear mortar frictional constraints
Default:1
C++ Type:double
Controllable:No
Description:Numerical parameter for nonlinear mortar frictional constraints
capture_tolerance0Normal distance from surface within which nodes are captured. This parameter is used for node-face and mortar formulations.
Default:0
C++ Type:double
Controllable:No
Description:Normal distance from surface within which nodes are captured. This parameter is used for node-face and mortar formulations.
correct_edge_droppingFalseWhether to enable correct edge dropping treatment for mortar constraints. When disabled any Lagrange Multiplier degree of freedom on a secondary element without full primary contributions will be set (strongly) to 0.
Default:False
C++ Type:bool
Controllable:No
Description:Whether to enable correct edge dropping treatment for mortar constraints. When disabled any Lagrange Multiplier degree of freedom on a secondary element without full primary contributions will be set (strongly) to 0.
displacementsThe displacements appropriate for the simulation geometry and coordinate system
C++ Type:std::vector<VariableName>
Controllable:No
Description:The displacements appropriate for the simulation geometry and coordinate system
formulationkinematicThe contact formulation
Default:kinematic
C++ Type:MooseEnum
Options:ranfs, kinematic, penalty, augmented_lagrange, tangential_penalty, mortar
Controllable:No
Description:The contact formulation
friction_coefficient0The friction coefficient
Default:0
C++ Type:double
Controllable:No
Description:The friction coefficient
generate_mortar_meshTrueWhether to generate the mortar mesh from the action. Typically this will be the case, but one may also want to reuse an existing lower-dimensional mesh prior to a restart.
Default:True
C++ Type:bool
Controllable:No
Description:Whether to generate the mortar mesh from the action. Typically this will be the case, but one may also want to reuse an existing lower-dimensional mesh prior to a restart.
inactiveIf specified blocks matching these identifiers will be skipped.
C++ Type:std::vector<std::string>
Controllable:No
Description:If specified blocks matching these identifiers will be skipped.
interpolate_normalsTrueWhether to interpolate the nodal normals for a mortar contact constraint (e.g. classic idea of evaluating field at quadrature points). If this is set to false, then non-interpolated nodal normals will be used, and then the _normals member should be indexed with _i instead of _qp. This input parameter is intended for developers.
Default:True
C++ Type:bool
Controllable:No
Description:Whether to interpolate the nodal normals for a mortar contact constraint (e.g. classic idea of evaluating field at quadrature points). If this is set to false, then non-interpolated nodal normals will be used, and then the _normals member should be indexed with _i instead of _qp. This input parameter is intended for developers.
mapped_primary_gap_offsetOffset to gap distance mapped from primary side
C++ Type:VariableName
Controllable:No
Description:Offset to gap distance mapped from primary side
modelfrictionlessThe contact model to use
Default:frictionless
C++ Type:MooseEnum
Options:frictionless, glued, coulomb
Controllable:No
Description:The contact model to use
mortar_dynamicsFalseWhether to use constraints that account for the persistency condition, giving rise to smoother normal contact pressure evolution. This flag should only be set to yes for dynamic simulations using the Newmark-beta numerical integrator
Default:False
C++ Type:bool
Controllable:No
Description:Whether to use constraints that account for the persistency condition, giving rise to smoother normal contact pressure evolution. This flag should only be set to yes for dynamic simulations using the Newmark-beta numerical integrator
newmark_beta0.25Newmark-beta beta parameter for its inclusion in the weighted gap update formula
Default:0.25
C++ Type:double
Controllable:No
Description:Newmark-beta beta parameter for its inclusion in the weighted gap update formula
newmark_gamma0.5Newmark-beta gamma parameter for its inclusion in the weighted gap update formula
Default:0.5
C++ Type:double
Controllable:No
Description:Newmark-beta gamma parameter for its inclusion in the weighted gap update formula
normal_lm_scaling1Scaling factor to apply to the normal LM variable for a mortar formulation
Default:1
C++ Type:double
Controllable:No
Description:Scaling factor to apply to the normal LM variable for a mortar formulation
normal_smoothing_distanceDistance from edge in parametric coordinates over which to smooth contact normal
C++ Type:double
Controllable:No
Description:Distance from edge in parametric coordinates over which to smooth contact normal
normal_smoothing_methodMethod to use to smooth normals
C++ Type:MooseEnum
Options:edge_based, nodal_normal_based
Controllable:No
Description:Method to use to smooth normals
normalize_cFalseWhether to normalize c by weighting function norm for mortar contact. When unnormalized the value of c effectively depends on element size since in the constraint we compare nodal Lagrange Multiplier values to integrated gap values (LM nodal value is independent of element size, where integrated values are dependent on element size).
Default:False
C++ Type:bool
Controllable:No
Description:Whether to normalize c by weighting function norm for mortar contact. When unnormalized the value of c effectively depends on element size since in the constraint we compare nodal Lagrange Multiplier values to integrated gap values (LM nodal value is independent of element size, where integrated values are dependent on element size).
normalize_penaltyFalseWhether to normalize the penalty parameter with the nodal area.
Default:False
C++ Type:bool
Controllable:No
Description:Whether to normalize the penalty parameter with the nodal area.
penalty1e+08The penalty to apply. This can vary depending on the stiffness of your materials
Default:1e+08
C++ Type:double
Controllable:No
Description:The penalty to apply. This can vary depending on the stiffness of your materials
ping_pong_protectionFalseWhether to protect against ping-ponging, e.g. the oscillation of the secondary node between two different primary faces, by tying the secondary node to the edge between the involved primary faces
Default:False
C++ Type:bool
Controllable:No
Description:Whether to protect against ping-ponging, e.g. the oscillation of the secondary node between two different primary faces, by tying the secondary node to the edge between the involved primary faces
primary_secondary_jacobianTrueWhether to include Jacobian entries coupling primary and secondary nodes.
Default:True
C++ Type:bool
Controllable:No
Description:Whether to include Jacobian entries coupling primary and secondary nodes.
secondary_gap_offsetOffset to gap distance from secondary side
C++ Type:VariableName
Controllable:No
Description:Offset to gap distance from secondary side
tangential_lm_scaling1Scaling factor to apply to the tangential LM variable for a mortar formulation
Default:1
C++ Type:double
Controllable:No
Description:Scaling factor to apply to the tangential LM variable for a mortar formulation
tangential_toleranceTangential distance to extend edges of contact surfaces
C++ Type:double
Controllable:No
Description:Tangential distance to extend edges of contact surfaces
tension_release0Tension release threshold. A node in contact will not be released if its tensile load is below this value. No tension release if negative.
Default:0
C++ Type:double
Controllable:No
Description:Tension release threshold. A node in contact will not be released if its tensile load is below this value. No tension release if negative.
use_dualFalseWhether to use the dual mortar approach within a mortar formulation. It is defaulted to true for weighted quantity approach, and to false for the legacy approach. To avoid instabilities in the solution and obtain the full benefits of a variational enforcement,use of dual mortar with weighted constraints is strongly recommended. This input is only intended for advanced users.
Default:False
C++ Type:bool
Controllable:No
Description:Whether to use the dual mortar approach within a mortar formulation. It is defaulted to true for weighted quantity approach, and to false for the legacy approach. To avoid instabilities in the solution and obtain the full benefits of a variational enforcement,use of dual mortar with weighted constraints is strongly recommended. This input is only intended for advanced users.

Optional Parameters

(modules/contact/test/tests/multiple_contact_pairs/multiple_pairs.i)

starting_point = 2e-1
offset = 1e-2

[GlobalParams]
  displacements = 'disp_x disp_y'
[]

[Mesh]
  file = multiple_pairs.e
[]

[Modules/TensorMechanics/Master]
  [all]
    add_variables = true
    strain = FINITE
    generate_output = 'stress_xx'
  []
[]

[Materials]
  [stiffStuff]
    type = ComputeIsotropicElasticityTensor
    block = '1 2 3'
    youngs_modulus = 1e6
    poissons_ratio = 0.3
  []
  [stiffStuff_stress]
    type = ComputeFiniteStrainElasticStress
    block = '1 2 3'
  []
[]

[ICs]
  [disp_y]
    block = '2 3'
    variable = disp_y
    value = '${fparse starting_point + offset}'
    type = ConstantIC
  []
[]

[Contact]
  [action_name]
    primary = '20 20'
    secondary = '10 101'
    penalty = 1e7
    formulation = penalty
    tangential_tolerance = 0.0001
  []
[]

[BCs]
  [botx]
    type = DirichletBC
    variable = disp_x
    preset = false
    boundary = 40
    value = 0.0
  []
  [boty]
    type = DirichletBC
    variable = disp_y
    preset = false
    boundary = 40
    value = 0.0
  []
  [topy]
    type = FunctionDirichletBC
    variable = disp_y
    preset = false
    boundary = '30 301'
    function = '${starting_point} * cos(2 * pi / 40 * t) + ${offset}'
  []
  [leftx]
    type = FunctionDirichletBC
    variable = disp_x
    preset = false
    boundary = '50 501'
    function = '1e-2 * t'
  []
[]

[Executioner]
  type = Transient
  end_time = 60
  dt = 2.0
  dtmin = .1
  solve_type = 'PJFNK'
  petsc_options = '-snes_converged_reason -ksp_converged_reason -pc_svd_monitor '
                  '-snes_linesearch_monitor'
  petsc_options_iname = '-pc_type -pc_factor_shift_type -pc_factor_shift_amount -mat_mffd_err'
  petsc_options_value = 'lu       NONZERO               1e-15                   1e-5'
  l_max_its = 30
  nl_max_its = 20
  nl_abs_tol = 1e-9
  line_search = 'none'
  snesmf_reuse_base = false
[]

[Debug]
  show_var_residual_norms = true
[]

[Outputs]
  exodus = true
  csv = true
[]

[Preconditioning]
  [smp]
    type = SMP
    full = true
  []
[]

[Postprocessors]
  active = 'num_nl cumulative'
  [num_nl]
    type = NumNonlinearIterations
  []
  [cumulative]
    type = CumulativeValuePostprocessor
    postprocessor = num_nl
  []
[]

[VectorPostprocessors]
  [cont_press]
    type = NodalValueSampler
    variable = contact_pressure
    boundary = '10 101'
    sort_by = x
    execute_on = NONLINEAR
  []
[]

(modules/contact/test/tests/sliding_block/sliding/frictionless_kinematic.i)

#  This is a benchmark test that checks constraint based frictionless
#  contact using the kinematic method.  In this test a constant
#  displacement is applied in the horizontal direction to simulate
#  a small block come sliding down a larger block.
#
#  The gold file is run on one processor
#  and the benchmark case is run on a minimum of 4 processors to ensure no
#  parallel variability in the contact pressure and penetration results.
#

[Mesh]
  file = sliding_elastic_blocks_2d.e
  patch_size = 80
[]

[GlobalParams]
  volumetric_locking_correction = false
  displacements = 'disp_x disp_y'
[]

[AuxVariables]
  [./penetration]
  [../]
  [./inc_slip_x]
  [../]
  [./inc_slip_y]
  [../]
  [./accum_slip_x]
  [../]
  [./accum_slip_y]
  [../]
[]

[Functions]
  [./vertical_movement]
    type = ParsedFunction
    value = -t
  [../]
[]

[Modules/TensorMechanics/Master]
  [./all]
    add_variables = true
    strain = FINITE
  [../]
[]

[AuxKernels]
  [./zeroslip_x]
    type = ConstantAux
    variable = inc_slip_x
    boundary = 3
    execute_on = timestep_begin
    value = 0.0
  [../]
  [./zeroslip_y]
    type = ConstantAux
    variable = inc_slip_y
    boundary = 3
    execute_on = timestep_begin
    value = 0.0
  [../]
  [./accum_slip_x]
    type = AccumulateAux
    variable = accum_slip_x
    accumulate_from_variable = inc_slip_x
    execute_on = timestep_end
  [../]
  [./accum_slip_y]
    type = AccumulateAux
    variable = accum_slip_y
    accumulate_from_variable = inc_slip_y
    execute_on = timestep_end
  [../]
  [./penetration]
    type = PenetrationAux
    variable = penetration
    boundary = 3
    paired_boundary = 2
  [../]
[]

[Postprocessors]
  [./nonlinear_its]
    type = NumNonlinearIterations
    execute_on = timestep_end
  [../]
  [./penetration]
    type = NodalVariableValue
    variable = penetration
    nodeid = 222
  [../]
  [./contact_pressure]
    type = NodalVariableValue
    variable = contact_pressure
    nodeid = 222
  [../]
[]

[BCs]
  [./left_x]
    type = DirichletBC
    variable = disp_x
    boundary = 1
    value = 0.0
  [../]
  [./left_y]
    type = DirichletBC
    variable = disp_y
    boundary = 1
    value = 0.0
  [../]
  [./right_x]
    type = DirichletBC
    variable = disp_x
    boundary = 4
    value = -0.02
  [../]
  [./right_y]
    type = FunctionDirichletBC
    variable = disp_y
    boundary = 4
    function = vertical_movement
  [../]
[]

[Materials]

  [./left]
    type = ComputeIsotropicElasticityTensor
    block = '1 2'
    youngs_modulus = 1e6
    poissons_ratio = 0.3
  [../]
  [./left_stress]
    type = ComputeFiniteStrainElasticStress
    block = '1 2'
  [../]
[]

[Executioner]
  type = Transient
  solve_type = 'PJFNK'

  petsc_options = '-snes_ksp_ew'
  petsc_options_iname = '-pc_type -sub_pc_type -pc_asm_overlap -ksp_gmres_restart'
  petsc_options_value = 'asm     lu    20    101'

  line_search = 'none'

  l_max_its = 100
  nl_max_its = 1000
  dt = 0.1
  end_time = 15
  num_steps = 1000
  l_tol = 1e-6
  nl_rel_tol = 1e-10
  nl_abs_tol = 1e-6
  dtmin = 0.01

  [./Predictor]
    type = SimplePredictor
    scale = 1.0
  [../]
[]

[Outputs]
  interval = 10
  [./out]
    type = Exodus
    elemental_as_nodal = true
  [../]
  [./console]
    type = Console
    max_rows = 5
  [../]
[]

[Contact]
  [./leftright]
    secondary = 3
    primary = 2
    model = frictionless
    penalty = 1e+6
    normal_smoothing_distance = 0.1
  [../]
[]

(modules/contact/test/tests/sliding_block/sliding/frictional_02_penalty.i)

#  This is a benchmark test that checks constraint based frictional
#  contact using the penalty method.  In this test a constant
#  displacement is applied in the horizontal direction to simulate
#  a small block come sliding down a larger block.
#
#  A friction coefficient of 0.2 is used.  The gold file is run on one processor
#  and the benchmark case is run on a minimum of 4 processors to ensure no
#  parallel variability in the contact pressure and penetration results.
#

[Mesh]
  file = sliding_elastic_blocks_2d.e
  patch_size = 80
[]

[GlobalParams]
  volumetric_locking_correction = false
  displacements = 'disp_x disp_y'
[]

[AuxVariables]
  [./penetration]
  [../]
  [./inc_slip_x]
  [../]
  [./inc_slip_y]
  [../]
  [./accum_slip_x]
  [../]
  [./accum_slip_y]
  [../]
[]

[Functions]
  [./vertical_movement]
    type = ParsedFunction
    value = -t
  [../]
[]

[Modules/TensorMechanics/Master]
  [./all]
    add_variables = true
    strain = FINITE
  [../]
[]

[AuxKernels]
  [./zeroslip_x]
    type = ConstantAux
    variable = inc_slip_x
    boundary = 3
    execute_on = timestep_begin
    value = 0.0
  [../]
  [./zeroslip_y]
    type = ConstantAux
    variable = inc_slip_y
    boundary = 3
    execute_on = timestep_begin
    value = 0.0
  [../]
  [./accum_slip_x]
    type = AccumulateAux
    variable = accum_slip_x
    accumulate_from_variable = inc_slip_x
    execute_on = timestep_end
  [../]
  [./accum_slip_y]
    type = AccumulateAux
    variable = accum_slip_y
    accumulate_from_variable = inc_slip_y
    execute_on = timestep_end
  [../]
  [./penetration]
    type = PenetrationAux
    variable = penetration
    boundary = 3
    paired_boundary = 2
  [../]
[]

[Postprocessors]
  [./nonlinear_its]
    type = NumNonlinearIterations
    execute_on = timestep_end
  [../]
  [./penetration]
    type = NodalVariableValue
    variable = penetration
    nodeid = 222
  [../]
  [./contact_pressure]
    type = NodalVariableValue
    variable = contact_pressure
    nodeid = 222
  [../]
[]

[BCs]
  [./left_x]
    type = DirichletBC
    variable = disp_x
    boundary = 1
    value = 0.0
  [../]
  [./left_y]
    type = DirichletBC
    variable = disp_y
    boundary = 1
    value = 0.0
  [../]
  [./right_x]
    type = DirichletBC
    variable = disp_x
    boundary = 4
    value = -0.02
  [../]
  [./right_y]
    type = FunctionDirichletBC
    variable = disp_y
    boundary = 4
    function = vertical_movement
  [../]
[]

[Materials]
  [./left]
    type = ComputeIsotropicElasticityTensor
    block = '1 2'
    youngs_modulus = 1e6
    poissons_ratio = 0.3
  [../]
  [./stress]
    type = ComputeFiniteStrainElasticStress
    block = '1 2'
  [../]
[]


[Executioner]
  type = Transient
  solve_type = 'PJFNK'

  petsc_options = '-snes_ksp_ew'
  petsc_options_iname = '-pc_type -pc_factor_mat_solver_type'
  petsc_options_value = 'lu     superlu_dist'

  line_search = 'none'

  l_max_its = 100
  nl_max_its = 1000
  dt = 0.1
  end_time = 15
  num_steps = 1000
  l_tol = 1e-6
  nl_rel_tol = 1e-10
  nl_abs_tol = 1e-6
  dtmin = 0.01

  [./Predictor]
    type = SimplePredictor
    scale = 1.0
  [../]
[]

[Outputs]
  interval = 10
  [./out]
    type = Exodus
    elemental_as_nodal = true
  [../]
  [./console]
    type = Console
    max_rows = 5
  [../]
[]

[Contact]
  [./leftright]
    secondary = 3
    primary = 2
    model = coulomb
    penalty = 1e+7
    friction_coefficient = 0.2
    formulation = penalty
    normal_smoothing_distance = 0.1
  [../]
[]

(modules/contact/test/tests/bouncing-block-contact/ping-ponging/mortar-no-ping-pong_weighted.i)

starting_point = 2e-1
offset = 1e-2

[GlobalParams]
  displacements = 'disp_x disp_y'
[]

[Mesh]
  [file]
    type = FileMeshGenerator
    file = long-bottom-block-no-lower-d.e
  []
[]

[Variables]
  [disp_x]
  []
  [disp_y]
  []
[]

[ICs]
  [disp_y]
    block = 2
    variable = disp_y
    value = '${fparse starting_point + offset}'
    type = ConstantIC
  []
[]

[Modules/TensorMechanics/Master]
  [all]
    add_variables = false
    use_automatic_differentiation = true
    strain = SMALL
  []
[]

[Materials]
  [elasticity]
    type = ADComputeIsotropicElasticityTensor
    youngs_modulus = 1e0
    poissons_ratio = 0.3
  []
  [stress]
    type = ADComputeLinearElasticStress
  []
[]

[Contact]
  [leftright]
    secondary = 10
    primary = 20
    model = frictionless
    formulation = mortar
    c_normal = 1e-1
  []
[]

[BCs]
  [botx]
    type = DirichletBC
    variable = disp_x
    boundary = 40
    value = 0.0
  []
  [boty]
    type = DirichletBC
    variable = disp_y
    boundary = 40
    value = 0.0
  []
  [topy]
    type = FunctionDirichletBC
    variable = disp_y
    boundary = 30
    function = '${starting_point} * cos(2 * pi / 40 * t) + ${offset}'
  []
  [leftx]
    type = FunctionDirichletBC
    variable = disp_x
    boundary = 50
    function = '1e-2 * t'
  []
[]

[Executioner]
  type = Transient
  num_steps = 40
  end_time = 200
  dt = 5
  dtmin = 5
  solve_type = 'PJFNK'
  petsc_options = '-snes_converged_reason -ksp_converged_reason -snes_ksp_ew'
  petsc_options_iname = '-pc_type -mat_mffd_err -pc_factor_shift_type'
  petsc_options_value = 'lu       1e-5          NONZERO'
  l_max_its = 30
  nl_max_its = 20
  nl_abs_tol = 1e-10
  nl_rel_tol = 1e-10
  line_search = 'none'
  snesmf_reuse_base = true
[]

[Debug]
  show_var_residual_norms = true
[]

[Outputs]
  [exo]
    type = Exodus
  []
[]

[Preconditioning]
  [smp]
    type = SMP
    full = true
  []
[]

(modules/contact/test/tests/3d-mortar-contact/frictional-mortar-3d-action.i)

starting_point = 0.25
offset = 0.00

[GlobalParams]
  displacements = 'disp_x disp_y disp_z'
  volumetric_locking_correction = true
[]

[Mesh]
  [top_block]
    type = GeneratedMeshGenerator
    dim = 3
    nx = 3
    ny = 3
    nz = 3
    xmin = -0.25
    xmax = 0.25
    ymin = -0.25
    ymax = 0.25
    zmin = -0.25
    zmax = 0.25
    elem_type = HEX8
  []
  [rotate_top_block]
    type = TransformGenerator
    input = top_block
    transform = ROTATE
    vector_value = '0 0 0'
  []
  [top_block_sidesets]
    type = RenameBoundaryGenerator
    input = rotate_top_block
    old_boundary = '0 1 2 3 4 5'
    new_boundary = 'top_bottom top_back top_right top_front top_left top_top'
  []
  [top_block_id]
    type = SubdomainIDGenerator
    input = top_block_sidesets
    subdomain_id = 1
  []
  [bottom_block]
    type = GeneratedMeshGenerator
    dim = 3
    nx = 10
    ny = 10
    nz = 2
    xmin = -.5
    xmax = .5
    ymin = -.5
    ymax = .5
    zmin = -.3
    zmax = -.25
    elem_type = HEX8
  []
  [bottom_block_id]
    type = SubdomainIDGenerator
    input = bottom_block
    subdomain_id = 2
  []
  [bottom_block_change_boundary_id]
    type = RenameBoundaryGenerator
    input = bottom_block_id
    old_boundary = '0 1 2 3 4 5'
    new_boundary = '100 101 102 103 104 105'
  []
  [combined]
    type = MeshCollectionGenerator
    inputs = 'top_block_id bottom_block_change_boundary_id'
  []
  [block_rename]
    type = RenameBlockGenerator
    input = combined
    old_block = '1 2'
    new_block = 'top_block bottom_block'
  []
  [bottom_right_sideset]
    type = SideSetsAroundSubdomainGenerator
    input = block_rename
    new_boundary = bottom_right
    block = bottom_block
    normal = '1 0 0'
  []
  [bottom_left_sideset]
    type = SideSetsAroundSubdomainGenerator
    input = bottom_right_sideset
    new_boundary = bottom_left
    block = bottom_block
    normal = '-1 0 0'
  []
  [bottom_top_sideset]
    type = SideSetsAroundSubdomainGenerator
    input = bottom_left_sideset
    new_boundary = bottom_top
    block = bottom_block
    normal = '0 0 1'
  []
  [bottom_bottom_sideset]
    type = SideSetsAroundSubdomainGenerator
    input = bottom_top_sideset
    new_boundary = bottom_bottom
    block = bottom_block
    normal = '0  0 -1'
  []
  [bottom_front_sideset]
    type = SideSetsAroundSubdomainGenerator
    input = bottom_bottom_sideset
    new_boundary = bottom_front
    block = bottom_block
    normal = '0 1 0'
  []
  [bottom_back_sideset]
    type = SideSetsAroundSubdomainGenerator
    input = bottom_front_sideset
    new_boundary = bottom_back
    block = bottom_block
    normal = '0 -1 0'
  []
  allow_renumbering = false
[]

[Modules/TensorMechanics/Master]
  [all]
    add_variables = true
    strain = FINITE
    block = '1 2'
    use_automatic_differentiation = false
    generate_output = 'stress_xx stress_xy stress_xz stress_yy stress_zz'
  []
[]

[Materials]
  [tensor]
    type = ComputeIsotropicElasticityTensor
    block = '1'
    youngs_modulus = 1.0e4
    poissons_ratio = 0.0
  []
  [stress]
    type = ComputeFiniteStrainElasticStress
    block = '1'
  []

  [tensor_1000]
    type = ComputeIsotropicElasticityTensor
    block = '2'
    youngs_modulus = 1e5
    poissons_ratio = 0.0
  []
  [stress_1000]
    type = ComputeFiniteStrainElasticStress
    block = '2'
  []
[]

[Contact]
  [mortar]
    primary = 'bottom_top'
    secondary = 'top_bottom'
    formulation = mortar
    model = coulomb
    friction_coefficient = 0.4
    c_normal = 1e4
    c_tangential = 1.0e4
    interpolate_normals = false
  []
[]

[BCs]
  [botx]
    type = DirichletBC
    variable = disp_x
    boundary = 'bottom_left bottom_right bottom_front bottom_back'
    value = 0.0
  []
  [boty]
    type = DirichletBC
    variable = disp_y
    boundary = 'bottom_left bottom_right bottom_front bottom_back'
    value = 0.0
  []
  [botz]
    type = DirichletBC
    variable = disp_z
    boundary = 'bottom_left bottom_right bottom_front bottom_back'
    value = 0.0
  []
  [topx]
    type = DirichletBC
    variable = disp_x
    boundary = 'top_top'
    value = 0.0
  []
  [topy]
    type = DirichletBC
    variable = disp_y
    boundary = 'top_top'
    value = 0.0
  []
  [topz]
    type = FunctionDirichletBC
    variable = disp_z
    boundary = 'top_top'
    function = '-${starting_point} * sin(2 * pi / 40 * t) + ${offset}'
  []
[]

[Executioner]
  type = Transient
  end_time = .025
  dt = .025
  dtmin = .001
  solve_type = 'PJFNK'
  petsc_options = '-snes_converged_reason -ksp_converged_reason -snes_ksp_ew'
  petsc_options_iname = '-pc_type -pc_factor_mat_solver_type -pc_factor_shift_type -pc_factor_shift_amount -mat_mffd_err'
  petsc_options_value = 'lu       superlu_dist                  NONZERO               1e-14                  1e-5'
  l_max_its = 15
  nl_max_its = 30
  nl_rel_tol = 1e-11
  nl_abs_tol = 1e-12
  line_search = 'basic'
[]

[Debug]
  show_var_residual_norms = true
[]

[Outputs]
  exodus = true
  csv = true
[]

[Preconditioning]
  [smp]
    type = SMP
    full = true
  []
[]

[Postprocessors]
  active = 'num_nl cumulative contact'
  [num_nl]
    type = NumNonlinearIterations
  []
  [cumulative]
    type = CumulativeValuePostprocessor
    postprocessor = num_nl
  []
  [contact]
    type = ContactDOFSetSize
    variable = mortar_normal_lm
    subdomain = 'mortar_secondary_subdomain'
    execute_on = 'nonlinear timestep_end'
  []
[]

[VectorPostprocessors]
  [contact-pressure]
    type = NodalValueSampler
    block = mortar_secondary_subdomain
    variable = mortar_normal_lm
    sort_by = 'id'
    execute_on = NONLINEAR
  []
  [frictional-pressure]
    type = NodalValueSampler
    block = mortar_secondary_subdomain
    variable = mortar_tangential_lm
    sort_by = 'id'
    execute_on = NONLINEAR
  []
  [frictional-pressure-3d]
    type = NodalValueSampler
    block = mortar_secondary_subdomain
    variable = mortar_tangential_3d_lm
    sort_by = 'id'
    execute_on = NONLINEAR
  []
  [tangent_x]
    type = NodalValueSampler
    block = mortar_secondary_subdomain
    variable = mortar_tangent_x
    sort_by = 'id'
    execute_on = NONLINEAR
  []
  [tangent_y]
    type = NodalValueSampler
    block = mortar_secondary_subdomain
    variable = mortar_tangent_y
    sort_by = 'id'
    execute_on = NONLINEAR
  []
[]

(modules/contact/test/tests/mechanical_constraint/frictionless_kinematic_gap_offsets.i)

# this test is the same as frictionless_kinematic test but designed to test the gap offset capability
# gap offsets with value of 0.01 were introduced to both primary and secondary sides in the initial mesh
# these values were accounted using the gap offset capability to produce the same result as if no gap offsets were introduced
[Mesh]
  file = blocks_2d_gap_offset.e
[]

[GlobalParams]
  displacements = 'disp_x disp_y'
[]

[AuxVariables]
  [./inc_slip_x]
  [../]
  [./inc_slip_y]
  [../]
  [./accum_slip_x]
  [../]
  [./accum_slip_y]
  [../]
  [./primary_gap_offset]
  [../]
  [./secondary_gap_offset]
  [../]
  [./mapped_primary_gap_offset]
  [../]
[]

[Functions]
  [./vertical_movement]
    type = ParsedFunction
    value = -t
  [../]
[]

[Modules/TensorMechanics/Master]
  [./all]
    add_variables = true
    strain = FINITE
  [../]
[]

[AuxKernels]
  [./zeroslip_x]
    type = ConstantAux
    variable = inc_slip_x
    boundary = 3
    execute_on = timestep_begin
    value = 0.0
  [../]
  [./zeroslip_y]
    type = ConstantAux
    variable = inc_slip_y
    boundary = 3
    execute_on = timestep_begin
    value = 0.0
  [../]
  [./accum_slip_x]
    type = AccumulateAux
    variable = accum_slip_x
    accumulate_from_variable = inc_slip_x
    execute_on = timestep_end
  [../]
  [./accum_slip_y]
    type = AccumulateAux
    variable = accum_slip_y
    accumulate_from_variable = inc_slip_y
    execute_on = timestep_end
  [../]
  [./primary_gap_offset]
    type = ConstantAux
    variable = primary_gap_offset
    value = -0.01
    boundary = 2
  [../]
  [./mapped_primary_gap_offset]
    type = GapValueAux
    variable = mapped_primary_gap_offset
    paired_variable = primary_gap_offset
    boundary = 3
    paired_boundary = 2
  [../]
  [./secondary_gap_offset]
    type = ConstantAux
    variable = secondary_gap_offset
    value = -0.01
    boundary = 3
  [../]
[]

[BCs]
  [./left_x]
    type = DirichletBC
    variable = disp_x
    boundary = 1
    value = 0.0
  [../]
  [./left_y]
    type = DirichletBC
    variable = disp_y
    boundary = 1
    value = 0.0
  [../]
  [./right_x]
    type = DirichletBC
    variable = disp_x
    boundary = 4
    value = -0.02
  [../]
  [./right_y]
    type = FunctionDirichletBC
    variable = disp_y
    boundary = 4
    function = vertical_movement
  [../]
[]

[Materials]
  [./left]
    type = ComputeIsotropicElasticityTensor
    block = 1
    poissons_ratio = 0.3
    youngs_modulus = 1e7
  [../]
  [./right]
    type = ComputeIsotropicElasticityTensor
    block = 2
    poissons_ratio = 0.3
    youngs_modulus = 1e6
  [../]
  [./stress]
    type = ComputeFiniteStrainElasticStress
    block = '1 2'
  [../]
[]

[Executioner]
  type = Transient

  solve_type = 'PJFNK'

  petsc_options_iname = '-pc_type'
  petsc_options_value = 'lu'

  line_search = 'none'

  l_max_its = 100
  nl_max_its = 1000
  dt = 0.01
  end_time = 0.10
  num_steps = 1000
  l_tol = 1e-6
  nl_rel_tol = 1e-10
  nl_abs_tol = 1e-8
  dtmin = 0.01

  [./Predictor]
    type = SimplePredictor
    scale = 1.0
  [../]
[]

[Outputs]
  file_base = frictionless_kinematic_gap_offsets_out
  [./exodus]
    type = Exodus
    elemental_as_nodal = true
  [../]
  [./console]
    type = Console
    max_rows = 5
  [../]
[]

[Contact]
  [./leftright]
    primary = 2
    secondary = 3
    model = frictionless
    penalty = 1e+6
    secondary_gap_offset = secondary_gap_offset
    mapped_primary_gap_offset = mapped_primary_gap_offset
  [../]
[]

Description
Constructed Objects
Notes on Node / Face Contact Enforcement
Parameter System
Gap offset parameters
Multiple contact pairs
Example Input syntax
Input Parameters

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Contact

Description

Constructed Objects

Notes on Node/Face Contact Enforcement

`System` Parameter

Gap offset parameters

Multiple contact pairs

Example Input syntax

Input Parameters

Required Parameters

Optional Parameters

Contact

Description

Constructed Objects

Notes on Node/Face Contact Enforcement

System Parameter

Gap offset parameters

Multiple contact pairs

Example Input syntax

Input Parameters

Required Parameters

Optional Parameters

(modules/contact/test/tests/multiple_contact_pairs/multiple_pairs.i)

(modules/contact/test/tests/sliding_block/sliding/frictionless_kinematic.i)

(modules/contact/test/tests/sliding_block/sliding/frictional_02_penalty.i)

(modules/contact/test/tests/bouncing-block-contact/ping-ponging/mortar-no-ping-pong_weighted.i)

(modules/contact/test/tests/3d-mortar-contact/frictional-mortar-3d-action.i)

(modules/contact/test/tests/mechanical_constraint/frictionless_kinematic_gap_offsets.i)

`System` Parameter